/*
 *
 *  * Copyright (C) 2015 Square, Inc.
 *  *
 *  * Licensed under the Apache License, Version 2.0 (the "License");
 *  * you may not use this file except in compliance with the License.
 *  * You may obtain a copy of the License at
 *  *
 *  *      http://www.apache.org/licenses/LICENSE-2.0
 *  *
 *  * Unless required by applicable law or agreed to in writing, software
 *  * distributed under the License is distributed on an "AS IS" BASIS,
 *  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  * See the License for the specific language governing permissions and
 *  * limitations under the License.
 *
 */
package com.lark.oapi.okhttp.internal.tls;

import javax.security.auth.x500.X500Principal;

/**
 * A distinguished name (DN) parser. This parser only supports extracting a string value from a DN.
 * It doesn't support values in the hex-string style.
 */
final class DistinguishedNameParser {

    private final String dn;
    private final int length;
    private int pos;
    private int beg;
    private int end;

    /**
     * Temporary variable to store positions of the currently parsed item.
     */
    private int cur;

    /**
     * Distinguished name characters.
     */
    private char[] chars;

    DistinguishedNameParser(X500Principal principal) {
        // RFC2253 is used to ensure we get attributes in the reverse
        // order of the underlying ASN.1 encoding, so that the most
        // significant values of repeated attributes occur first.
        this.dn = principal.getName(X500Principal.RFC2253);
        this.length = this.dn.length();
    }

    // gets next attribute type: (ALPHA 1*keychar) / oid
    private String nextAT() {
        // skip preceding space chars, they can present after
        // comma or semicolon (compatibility with RFC 1779)
        for (; pos < length && chars[pos] == ' '; pos++) {
        }
        if (pos == length) {
            return null; // reached the end of DN
        }

        // mark the beginning of attribute type
        beg = pos;

        // attribute type chars
        pos++;
        for (; pos < length && chars[pos] != '=' && chars[pos] != ' '; pos++) {
            // we don't follow exact BNF syntax here:
            // accept any char except space and '='
        }
        if (pos >= length) {
            throw new IllegalStateException("Unexpected end of DN: " + dn);
        }

        // mark the end of attribute type
        end = pos;

        // skip trailing space chars between attribute type and '='
        // (compatibility with RFC 1779)
        if (chars[pos] == ' ') {
            for (; pos < length && chars[pos] != '=' && chars[pos] == ' '; pos++) {
            }

            if (chars[pos] != '=' || pos == length) {
                throw new IllegalStateException("Unexpected end of DN: " + dn);
            }
        }

        pos++; //skip '=' char

        // skip space chars between '=' and attribute value
        // (compatibility with RFC 1779)
        for (; pos < length && chars[pos] == ' '; pos++) {
        }

        // in case of oid attribute type skip its prefix: "oid." or "OID."
        // (compatibility with RFC 1779)
        if ((end - beg > 4) && (chars[beg + 3] == '.')
                && (chars[beg] == 'O' || chars[beg] == 'o')
                && (chars[beg + 1] == 'I' || chars[beg + 1] == 'i')
                && (chars[beg + 2] == 'D' || chars[beg + 2] == 'd')) {
            beg += 4;
        }

        return new String(chars, beg, end - beg);
    }

    // gets quoted attribute value: QUOTATION *( quotechar / pair ) QUOTATION
    private String quotedAV() {
        pos++;
        beg = pos;
        end = beg;
        while (true) {

            if (pos == length) {
                throw new IllegalStateException("Unexpected end of DN: " + dn);
            }

            if (chars[pos] == '"') {
                // enclosing quotation was found
                pos++;
                break;
            } else if (chars[pos] == '\\') {
                chars[end] = getEscaped();
            } else {
                // shift char: required for string with escaped chars
                chars[end] = chars[pos];
            }
            pos++;
            end++;
        }

        // skip trailing space chars before comma or semicolon.
        // (compatibility with RFC 1779)
        for (; pos < length && chars[pos] == ' '; pos++) {
        }

        return new String(chars, beg, end - beg);
    }

    // gets hex string attribute value: "#" hexstring
    private String hexAV() {
        if (pos + 4 >= length) {
            // encoded byte array  must be not less then 4 c
            throw new IllegalStateException("Unexpected end of DN: " + dn);
        }

        beg = pos; // store '#' position
        pos++;
        while (true) {

            // check for end of attribute value
            // looks for space and component separators
            if (pos == length || chars[pos] == '+' || chars[pos] == ','
                    || chars[pos] == ';') {
                end = pos;
                break;
            }

            if (chars[pos] == ' ') {
                end = pos;
                pos++;
                // skip trailing space chars before comma or semicolon.
                // (compatibility with RFC 1779)
                for (; pos < length && chars[pos] == ' '; pos++) {
                }
                break;
            } else if (chars[pos] >= 'A' && chars[pos] <= 'F') {
                chars[pos] += 32; //to low case
            }

            pos++;
        }

        // verify length of hex string
        // encoded byte array  must be not less then 4 and must be even number
        int hexLen = end - beg; // skip first '#' char
        if (hexLen < 5 || (hexLen & 1) == 0) {
            throw new IllegalStateException("Unexpected end of DN: " + dn);
        }

        // get byte encoding from string representation
        byte[] encoded = new byte[hexLen / 2];
        for (int i = 0, p = beg + 1; i < encoded.length; p += 2, i++) {
            encoded[i] = (byte) getByte(p);
        }

        return new String(chars, beg, hexLen);
    }

    // gets string attribute value: *( stringchar / pair )
    private String escapedAV() {
        beg = pos;
        end = pos;
        while (true) {
            if (pos >= length) {
                // the end of DN has been found
                return new String(chars, beg, end - beg);
            }

            switch (chars[pos]) {
                case '+':
                case ',':
                case ';':
                    // separator char has been found
                    return new String(chars, beg, end - beg);
                case '\\':
                    // escaped char
                    chars[end++] = getEscaped();
                    pos++;
                    break;
                case ' ':
                    // need to figure out whether space defines
                    // the end of attribute value or not
                    cur = end;

                    pos++;
                    chars[end++] = ' ';

                    for (; pos < length && chars[pos] == ' '; pos++) {
                        chars[end++] = ' ';
                    }
                    if (pos == length || chars[pos] == ',' || chars[pos] == '+'
                            || chars[pos] == ';') {
                        // separator char or the end of DN has been found
                        return new String(chars, beg, cur - beg);
                    }
                    break;
                default:
                    chars[end++] = chars[pos];
                    pos++;
            }
        }
    }

    // returns escaped char
    private char getEscaped() {
        pos++;
        if (pos == length) {
            throw new IllegalStateException("Unexpected end of DN: " + dn);
        }

        switch (chars[pos]) {
            case '"':
            case '\\':
            case ',':
            case '=':
            case '+':
            case '<':
            case '>':
            case '#':
            case ';':
            case ' ':
            case '*':
            case '%':
            case '_':
                //FIXME: escaping is allowed only for leading or trailing space char
                return chars[pos];
            default:
                // RFC doesn't explicitly say that escaped hex pair is
                // interpreted as UTF-8 char. It only contains an example of such DN.
                return getUTF8();
        }
    }

    // decodes UTF-8 char
    // see http://www.unicode.org for UTF-8 bit distribution table
    private char getUTF8() {
        int res = getByte(pos);
        pos++; //FIXME tmp

        if (res < 128) { // one byte: 0-7F
            return (char) res;
        } else if (res >= 192 && res <= 247) {

            int count;
            if (res <= 223) { // two bytes: C0-DF
                count = 1;
                res = res & 0x1F;
            } else if (res <= 239) { // three bytes: E0-EF
                count = 2;
                res = res & 0x0F;
            } else { // four bytes: F0-F7
                count = 3;
                res = res & 0x07;
            }

            int b;
            for (int i = 0; i < count; i++) {
                pos++;
                if (pos == length || chars[pos] != '\\') {
                    return 0x3F; //FIXME failed to decode UTF-8 char - return '?'
                }
                pos++;

                b = getByte(pos);
                pos++; //FIXME tmp
                if ((b & 0xC0) != 0x80) {
                    return 0x3F; //FIXME failed to decode UTF-8 char - return '?'
                }

                res = (res << 6) + (b & 0x3F);
            }
            return (char) res;
        } else {
            return 0x3F; //FIXME failed to decode UTF-8 char - return '?'
        }
    }

    // Returns byte representation of a char pair
    // The char pair is composed of DN char in
    // specified 'position' and the next char
    // According to BNF syntax:
    // hexchar    = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
    //                    / "a" / "b" / "c" / "d" / "e" / "f"
    private int getByte(int position) {
        if (position + 1 >= length) {
            throw new IllegalStateException("Malformed DN: " + dn);
        }

        int b1, b2;

        b1 = chars[position];
        if (b1 >= '0' && b1 <= '9') {
            b1 = b1 - '0';
        } else if (b1 >= 'a' && b1 <= 'f') {
            b1 = b1 - 87; // 87 = 'a' - 10
        } else if (b1 >= 'A' && b1 <= 'F') {
            b1 = b1 - 55; // 55 = 'A' - 10
        } else {
            throw new IllegalStateException("Malformed DN: " + dn);
        }

        b2 = chars[position + 1];
        if (b2 >= '0' && b2 <= '9') {
            b2 = b2 - '0';
        } else if (b2 >= 'a' && b2 <= 'f') {
            b2 = b2 - 87; // 87 = 'a' - 10
        } else if (b2 >= 'A' && b2 <= 'F') {
            b2 = b2 - 55; // 55 = 'A' - 10
        } else {
            throw new IllegalStateException("Malformed DN: " + dn);
        }

        return (b1 << 4) + b2;
    }

    /**
     * Parses the DN and returns the most significant attribute value for an attribute type, or null
     * if none found.
     *
     * @param attributeType attribute type to look for (e.g. "ca")
     */
    public String findMostSpecific(String attributeType) {
        // Initialize internal state.
        pos = 0;
        beg = 0;
        end = 0;
        cur = 0;
        chars = dn.toCharArray();

        String attType = nextAT();
        if (attType == null) {
            return null;
        }
        while (true) {
            String attValue = "";

            if (pos == length) {
                return null;
            }

            switch (chars[pos]) {
                case '"':
                    attValue = quotedAV();
                    break;
                case '#':
                    attValue = hexAV();
                    break;
                case '+':
                case ',':
                case ';': // compatibility with RFC 1779: semicolon can separate RDNs
                    //empty attribute value
                    break;
                default:
                    attValue = escapedAV();
            }

            // Values are ordered from most specific to least specific
            // due to the RFC2253 formatting. So take the first match
            // we see.
            if (attributeType.equalsIgnoreCase(attType)) {
                return attValue;
            }

            if (pos >= length) {
                return null;
            }

            if (chars[pos] == ',' || chars[pos] == ';') {
            } else if (chars[pos] != '+') {
                throw new IllegalStateException("Malformed DN: " + dn);
            }

            pos++;
            attType = nextAT();
            if (attType == null) {
                throw new IllegalStateException("Malformed DN: " + dn);
            }
        }
    }
}
